Rotary encoders of optical or magnetic construction are used to measure or sense rotation, typically of a shaft or the like, by providing rotational-related data from which information, such as absolute or relative rotary position can be determined. Rotary encoders are very versatile and used in applications that frequently require controlling the motion of a rotating object, such as a shaft or the like. Other applications include: monitoring motor feedback, cut-to-length applications, filling applications, backstop applications, robotics, etc.
Optical rotary encoders typically use a circular disk that has sections coded, such as by being blacked out or otherwise marked, that turns with the object whose rotary movement is being measured. A sensor reads light reflected from the disk in determining whether there has been a change in rotary position of the disk.
While optical rotary encoders have enjoyed a great deal of commercial success, they nonetheless suffer from numerous drawbacks. They are undesirably complicated, sensitive to dust, oil and dirt, mechanically fragile, typically cannot be used in relatively high temperature environments, and are susceptible to shock and vibration.
Magnetic rotary encoders have a construction that overcomes most, if not nearly all, of these disadvantages. However, in the past, magnetic rotary encoders require relatively precise axial and radial positioning of an encoder shaft-mounted magnet used to excite Hall Effect sensors that define a sensor region of a magnetic rotary encoder chip. Since the Hall sensors inside the encoder chip require a uniform magnetic field distribution, failure to maintain such precise exciter magnet location produces increased signal noise, causes positional error, or both, which obviously is highly undesirable.
What is therefore needed is a rotary magnetic encoder that does not suffer the drawbacks of rotary optical encoders but is more tolerant to encoder shaft misalignment than conventional rotary magnetic encoders.